Image-forming apparatus

Abstract

An image-forming apparatus is provided with: a photoconductor drum having a surface on which a toner image is formed, a transfer drum for transferring the toner image onto a copying material by allowing the copying material to contact the photoconductor drum, and a ground roller for electrostatically attracting the copying material onto the transfer drum prior to transferring the toner image onto the copying material. He transfer drum is constituted by a semi-conductive layer and a dielectric layer that are stacked on a conductive layer. [Supposing that] The nip width between the photoconductor drum and the transfer drum is L1, the rotation speed of the two drums is Vp, and the time constant, which is represented by a product of the resistance and the capacitance between the two drums, is τ, the relationship represented by L1/Vp<τ is satisfied. By defining the time constant of the transfer drum [as described above], it becomes possible to stabilize an electric field made by the transfer drum, and consequently to carry out a desired transferring operation.

What is claimed is: 
     
       1. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   transfer means for transferring the toner image formed on the image-bearing body onto a copying material by allowing the copying material to contact the image-bearing body the width of the contact being represented by L and the surface velocity or the image-bearing body being Vp, the transfer means being constituted by a dielectric layer that is stacked on a conductive base, the transfer means having a time constant τ equal to a product of the resistance and the capacitance between the image-bearing body and the transfer means so that the relationship represented by L/Vp<τ is satisfied; and   attracting means for electrically attracting and holding the copying material onto the transfer means prior to transferring the toner image onto a copying material, the attracting means being placed on the periphery of the transfer means.   
     
     
       2. The image-forming apparatus as defined in claim 1, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the transfer means. 
     
     
       3. The image-forming apparatus as defined in claim 1, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the transfer means, with a clearance being formed between the elastic resistor layer and the dielectric layer. 
     
     
       4. The image-forming apparatus as defined in claim 3, wherein the coefficient of thermal expansion of the elastic resistor layer is set greater than the coefficient of thermal expansion of the dielectric layer. 
     
     
       5. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed: intermediate transfer means on which the toner image formed on the image-bearing body is temporarily electrostatically transferred, the intermediate transfer means being constituted by a dialectric layer that is stacked on a conductive base; and   transfer means for electrostatically transferring the toner image that has been temporarily transferred onto the intermediate transfer means onto a copying material,   wherein the width of a contact portion formed by the contact between the image-bearing body and the intermediate transfer means is represented by L, the surface velocity of the image-bearing body and the intermediate transfer means is represented by Vp and the time constant of the intermediate transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the intermediate transfer means, is τ so that the relationship represented by L/Vp<τ is satisfied.     
     
     
       6. The image-forming apparatus as defined in claim 5, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the intermediate transfer means. 
     
     
       7. The image-forming apparatus as defined in claim 5, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the intermediate transfer means, with a clearance being formed between the elastic resistor layer and the dielectric layer. 
     
     
       8. The image-forming apparatus as defined in claim 7, wherein the coefficient of thermal expansion of the elastic resistor layer is set greater than the coefficient of thermal expansion of the dielectric layer. 
     
     
       9. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   transfer means, constituted by a dielectric layer that is stacked on a conductive base, for transferring the toner image formed on the image-bearing body onto a copying material by allowing the copying material electrostatically attracted onto the dielectric layer to contact the image-bearing body during the rotation thereof,   attracting means for eelctrostatically attracting the copying material onto the dielectric layer, the attracting means being placed on the upstream side of the transferring position on the periphery of the transfer means; and cleaning means for removing residual toner from the surface of the transfer means after separation of the copying material, the cleaning means being placed on the downstream side of the transferring position on the periphery of the transfer means,   wherein the distance on the circumferential surface of the transfer means from the cleaning position associated with the cleaning means to the attracting position associated with the attracting means is represented by L, the surface velocity of the image-bearing body and the transfer means is represented by Vp and the time constant of the transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the transfer means, is τ, so that the relationship represented by L/Vp>τ is satisfied.   
     
     
       10. The image-forming apparatus as defined in claim 9, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the transfer means. 
     
     
       11. The image-forming apparatus as defined in claim 9, further comprising: at least a layer of an elastic resistor that is placed between the conductive base and the dielectric layer in the transfer means, with a clearance being formed between the elastic resistor layer and the dielectric layer. 
     
     
       12. The image-forming apparatus as defined in claim 11, wherein the coefficient of thermal expansion of the elastic resistor layer is set greater than the coefficient of thermal expansion of the dielectric layer. 
     
     
       13. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   transfer means for transferring the toner image formed on the image-bearing body onto a copying material by allowing the copying material to contact the image-bearing body, the transfer means being constituted by a dielectric layer that is stacked on a conductive base; and   attracting means for electrically attracting and holding the copying material onto the transfer means prior to transferring the toner image onto the copying material, the attracting means being placed on the periphery of the transfer means,   wherein the distance on the transfer means from the transferring position associated with the transfer means to the attracting position associated with the attracting means is represented by L, the surface velocity of the image-bearing body and the transfer means is represented by Vp and the time constant of the transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the transfer means, is τ, so that the relationship represented by L/Vp<τ is satisfied.   
     
     
       14. An image-forming apparatus comprising: an image bearing body having a surface on which a toner image is formed;   intermediate transfer means on which the toner image formed on the image-bearing body is temporarily electrostatically transferred, the intermediate transfer means being constituted by a dielectric layer that is stacked on a conductive base; and   transfer means for electrostatically transferring the toner image that has been temporarily transferred onto the intermediate transfer means onto a copying material.   wherein the distance on the intermediate transfer means from the first transferring position at which the toner image is transferred from the image-bearing body onto the intermediate transfer means to the second transferring position at which the toner image is transferred from the intermediate transfer means to the copying material is represented by L, the surface velocity of the image-bearing body and the intermediate transfer means is represented by Vp and the time constant of the intermediate transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the intermediate transfer means, is τ, so that the relationship represented by L/Vp<τ is satisfied.   
     
     
       15. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   transfer means for transferring the toner image formed on the image-bearing body onto a copying material by allowing the copying material to contact the image-bearing body, the transfer means being constituted by a dielectric layer that is stacked on a conductive base; and   attracting means for electrically attracting and holding the copying material onto the transfer means prior to transferring the toner image onto the copying material, the attracting means being placed on the periphery of the transfer means,   wherein the length of the circumference of the transfer means is represented by L, the surface velocity of the image-bearing body and the transfer means is represented by Vp and the time constant of the transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the transfer means, is τ, so that the relationship represented by L/Vp<τ is satisfied.   
     
     
       16. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   intermediate transfer means on which the toner image formed on the image-bearing body is temporarily electrostatically transferred, the intermediate transfer means being constituted by a dielectric layer that is stacked on a conductive base; and   transfer means for electrostatically transferring the toner image that has been temporarily transferred onto the intermediate transfer means onto a copying material,   wherein the length of the circumference of the intermediate transfer means is represented by L, the surface velocity of the image-bearing body and intermediate transfer means is represented by Vp and the time constant of the intermediate transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the intermediate transfer means, is τ, so that the relationship represented by L/Vp<τ is satisfied.   
     
     
       17. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   transfer means for transferring the toner image formed on the image-bearing body onto a copying material by allowing the copying material to contact the image-bearing body, the transfer means being constituted by a dielectric layer that is stacked on a conductive base; and   cleaning means for removing residual toner from the surface of the transfer means after the toner image has been transferred onto the copying material, the cleaning means being placed on the periphery of the transfer means,   wherein the distance on the transfer means from the transferring position associated with the transfer means to the cleaning position associated with the cleaning means is represented by L, the surface velocity of the image-bearing body and the transfer means is represented by Vp and the time constant of the transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the transfer means, is τ, so that the relationship represented by L/Vp>is satisfied.   
     
     
       18. An image-forming apparatus comprising: an image-bearing body having a surface on which a toner image is formed;   intermediate transfer means on which the toner image formed on the image-bearing body is temporarily electrostatically transferred, the intermediate transfer means being constituted by a dielectric layer that is stacked on a conductive base;   transfer means for electrostatically transferring the toner image that has been temporarily transferred onto the intermediate transfer means onto a copying material; and   cleaning means for removing residual toner from the surface of the intermediate transfer means after the toner image has been transferred onto the copying material, the cleaning means being placed on the periphery of the intermediate transfer means.   wherein the distance on the intermediate transfer means from the transferring position at which the toner image is transferred from the image-bearing body to the intermediate transfer means to the cleaning position associated with the cleaning means is represented by L, the surface velocity of the image-bearing body and the intermediate transfer means is represented by Vp and the time constant of the intermediate transfer means, which is represented by a product of the resistance and the capacitance between the image-bearing body and the intermediate transfer means, is τ, so that the relationship represented by L/Vp>τ is satisfied.